These entrepreneurs, interviewed by Forbes over the last three years, started launching businesses by the tender age of 9. Some of them identified problems and created companies to solve them, while others turned their hobbies into money-making ventures. Some teamed up with friends, parents and mentors; others plowed ahead on their own. To qualify for this round-up, the kids had to have cracked $1 million in revenue before college graduation and by age 22 (or be on track to do so), or had to have received funding that valued their operations at $1 million or more.

In the summer of 2008, after his high school graduation, Jason Brian started working in the marketing department of a South Florida car dealership. He knew the future of marketing was on the Web. "With half of the money, I found that I could double the results," by buying online ads and using search engine optimization techniques, he recalls. Three years later, at age 21, Brian spent "less than $10,000" of his savings to build a website that would help consumers look for cars. Autocricket.com made money by selling customers' information to dealers and manufacturers, which could market to customers directly. Six months after launch the site attracted the attention of two entrepreneurs in Naples, Fla., who invested $250,000. The site generated $1.2 million in revenue in 2009, when Brian was 22. In 2010 it did $6 million.

Showclix
In 2005, when he was 18, Joshua Dziabiak sold his first company--a Web hosting firm called Mediacatch--for north of $1 million. He bought a Mercedes (in cash) and a flat-screen TV, and used the rest to invest in other companies, including Showclix, his current venture, a website that lets performing arts centers, colleges, live music venues and other outlets sell tickets online, over the phone and at their box offices. In 2009 he raised nearly $1 million, which valued the company at $2.75 million. Showclix collects services fees (usually paid by the ticket buyer) of 7% to 15% of ticket sales. Those fees brought in $9 million last year.